Nebraska LTAP
Date of this Version
12-10-2023
Document Type
Article
Citation
Hu, J., Marcus, G., and Aitbayeva, A. (2023). "Production of Cast-in-Place UHPC for Bridge Applications". NDOT Research Report SPR‐FY22(008).
Abstract
This project presents a comprehensive overview of the essential aspects associated with the cast-in-place application of UHPC, including formwork requirements, surface preparation, mixing procedures, placing methods, curing techniques, grinding specifications, and mockup construction. Each section provides in-depth insights into specific guidelines and practices outlined by various regulatory bodies. The research team has developed training materials designed for a full-day workshop tailored to benefit both contractors and NDOT engineers. This workshop comprises key topics such as proportioning, batching, testing, and the placement of both non-proprietary and proprietary UHPC mixes, as well as hands-on experience in batching, testing, and placing UHPC. The study investigating fresh and hardened UHPC tests to identify fiber segregation reveals that excessive water or the use of high-range water-reducing admixtures (HRWR) can lead to fiber segregation, which is observable in both fresh and hardened states. Techniques such as Visual Stability Index (VSI) and Hardened Visual Stability Index (HVSI) are somewhat subjective, while tests like the mini-V-funnel and falling ball tests provide more objective measures. Flow time shows promise as an indicator of fiber stability, but further research and data are required to establish Quality Assurance/Quality Control (QA/QC) ranges. The study also underscores the potential of surface resistivity testing and calls for more extensive research to refine these tests for practical application in construction. The experimental work explores the influence of shrinkage-reducing admixtures (SRA) and shrinkage-compensating admixtures (SCA) on UHPC. Optimal SRA dosage effectively mitigates both total and autogenous shrinkage of UHPC, with total shrinkage decreasing from 817µɛ to 539µɛ and autogenous shrinkage dropping from 691µɛ to 437µɛ. The effectiveness of SCA varies, and its impact on shrinkage is significant under specific hot batch curing conditions, although such methods may not be feasible for all concrete applications. The report also included a draft of the special provision for cast-in-place (CIP) UHPC.